Method of fitting piping for a hot or cold fluid

ABSTRACT

A piping for a hot or a cold fluid may be exposed to harmful stresses when the fluid in the piping changes its temperature. So-called compensators have been used for reducing said stresses. According to the invention the compensators may be omitted if the piping is heated to a temperature between its minimum and maximum operating temperature before it is fixed in the desired position.

United States Patent Lundgren Jan. 29, 1974 METHOD OF FITTING PIPING FORA HOT [56] References Cited R COLD FLU") UNITED STATES PATENTS [75]Inventor: Jens Ove Lundgren, Orebro, 3,630,038 12/1971 Ando Sweden2,765,135 /1956 Che11is.....

3,169,576 2 1965 Le t 1 138 DIG. 5 [73] Assignee: Rorkonsult ForFjarrvarmei Orebro e e a Orebm Sweden Primary ExaminerJacob Shapiro [22]Filed: Nov. 15, 1971 Attorney, Agent, or Firm-Toren and McGeady 21 A 1.N 198 644 1 pp 0 57 ABSTRACT A piping for a hot or a cold fluid may beexposed to Forelgn Apphcauon Pnomy Data harmful stresses when the fluidin the piping changes Nov. 19, 1970 Sweden 15697/ its temperature. socalled compensators have been May 28, 1971 Sweden 6996/71 used forreducing Said stresses According to the vention the compensators may beomitted if the piping [52] US. Cl 61/72.1, 138/105, 248/49 is heated toa temperature between its minimumand [51] Int. Cl. F16] 27/00, F24d 3/00maximum operating temperature before it is fixed in [58] Field of Search61/721, 72.5, 72.7, 43; the desired position A 248/49; 138/DIG. 5,

3 Claims, 1 Drawing Figure METHOD OF FITTING PIPING FOR A HOT R COLDFLUID The invention relates to a method of fitting piping for a hot orcold fluid. The object of the invention is to be able to fit a metallicpipe which will be subjected to temperature variations, without usingso-called compensators or other devices which take up the expansion orcontraction of the pipe upon a temperature change.

Attempts have been made previously to avoid the use of compensators byfitting the piping at attachment points, for example concrete bases.This has been successful with small temperature variations, but forpipes having very high or very low working temperatures the stress hasbeen so great as the temperature increased that the pipe cracked or theyield point of the material was exceeded.

According to the invention it has now been found that the risk ofdeformation is eliminated if the piping is first heated or cooled to atemperature above. or below the normal temperature of the surroundingsand is then fixed in the desired position. The piping should be heatedor cooled to a temperature, in the'following called the fixingtemperature, which is between the minimum and the maximum workingtemperature of the fluid in the piping.

If the temperature in a pipe for a hot fluid exceeds the fixingtemperature, the pipe is subjected to a compressive strain. The fixingtemperature should be so close to the maximum working temperature thatthe pipe can tolerate the maximum compressive stress reached.

if the temperature in the piping falls below the fixing temperature thepiping will be subjected to a tensile stress. The lowest workingtemperature permitted should be chosen so that the tensile stressarising can be tolerated. If, for'example at a shut-down, the temperatueshows a tendency to fall so low that impermissible tensile stressesarise in the piping, it must be heated by blowing in steam or hot air,for example. If, for some reason, it is impossible to heat the piping inthis way it is better to cut the piping rather than allowing anuncontrolled rupture in the piping. When the piping is being repairedthe cut ends can be brought into contact by heating the piping, afterwhich they can be welded.

A similar condition prevails for piping for a cold fluid, but in thiscase the piping is cooled to a temperature below that of thesurroundings and is kept at this temperature during the fixingoperation. If a breakdown occurs the temperature of the pipe mayincrease to the normal temperature of the surroundings, and the fixingtemperature should therefore be so close to this normal temperature thatthe maximum compressive stress reached can be tolerated.

The pipe may be fixed in the desired position by being attached orfastened, at predetermined intervals, to attachment members. Saidmembers may preferably consist of concrete foundations. The pipingshould be loaded between the attachment members so that the compressivestress does not cause the pipe to crack. For piping laid under ground itshould be ascertained that the pressure of the earth is sufficientlyhigh. Attachment members may preferably be applied at pipe bends and atso-called pipe ends, that is where the pipe is provided with a shut-offvalve or the like.

According to another embodiment of the invention said attachment membersmay be omitted. The piping may be fixed in the desired position by beingplaced in a pipe trench in the ground. The earth is subsequentlyreplaced in the trench, thus surrounding the piping and fixing it in thedesired position. Such piping is held in place by so-called frictionpositioning, by which is meant that when tolerably small movements occurin the longitudinal direction of the piping due to temperaturevariations, there will be such friction between the piping and thesurrounding earth that the tension in the piping is held withinpermissible limits. When laying pipe in the ground, the piping is placedin the desired position in the pipe trench. It is then heated or cooledto the normal operating temperature or a temperature between the minimumand the maximum operating temperatures, after which earth'is replaced inthe pipe trench. The pressure of the earth must be so high that thepiping does noteven crack at the maximum compressive stresses occurring.

In the following the invention will be explained more fully withreference to the accompanying drawing which, by way of example, shows asection of a hot water pipe in a district heating plant. The pipe 1 is asocalled culvert pipe, that is to say it is surrounded by insulation andan outer casing. The pipe is laid in a trench in the ground at suchdepth that the ground pressure counteracts the cracking tendencyoccurring when the temperature exceeds the fixing temperature. The pipeis provided with two shut-off valves 2, 3 which are accessible downshafts 4, 5. An attachment member 6, in the form of a concretefoundation, is arranged close to the valve 2. A concrete foundation 9 isalso arranged to fix a branch pipe 10 for a heat consumer 12, close tothe place where the branch pipe 10 is connected to the main piping 1.

An attachment means 11, 13, is applied to the pipe in each attachmentmember 6, 9 when the piping is being fitted. The attachment means maycomprise wings, flanges, sections or the like, which are welded to thepipe. The piping is then heated, for exmple by its normal heat-transportfluid supplied from the heatproducing unit, steam or hot air, to thedesired fixing temperature, the pipe being allowed to expand freely. Theconcrete foundations 6, 9 are then cast around the attachment means 11,13, the earth is replaced into the trench, and the temperature ismaintained until the concrete has set. in operation, the main pipe 1 isfixed in the desired position by means of the pressure of the earthwhich has been replaced into the trench. The branch pipe 10 is fixedpartly by means of the pressure of the earth, partly by means of theconcrete foundation 9. Said concrete foundation 9, which is situatedclose to the main pipe 1, prevents the main pipe 1 from being exposed tolateral forces produced by the branch pipe 10. The concrete foundation 6is situated at a place where the main pipe 1 changes its direction froma horizontal direction to a slightly inclined direction. It prevents themain pipe 1 from moving in the vertical direction.

I claim:

1. Method of mounting a hot water pipe in a district heating system in afixed position for use in conveying hot water which flows through thepiping at an operating temperature range of minimum to maximumtemperatures above the ambient temperature, comprising the steps oflocating a continuous length of piping from a source to a point of use,bringing the piping to a temperature within the range of its operatingtemperature 3 by flowing hot water through the piping and permitting itto change length freely in response to the temperature to which it isheated by the hot water, and while maintaining the piping at thetemperature in its operating range, fixing the piping in the useposition.

2. Method, as set forth in claim 1, characterized by fixing the pipingin the use position by fastening it at predetermined intervals toconcrete attachment members.

3. Method of mounting a hot water pipe in a district heating system in afixed position for use in conveying hot water which flows through thepiping within an operating temperature range of minimum to maximumtemperatures above the ambient temperature, comprising the steps oflocating a continuous length of piping in a position for use within anexcavated earth trench from a source to a position of use, bringing thepiping to a temperature within the range of its operating temperature byflowing hot water through the piping and permitting it to change lengthfreely in response to the temperature to which it is heated by the hotwater, and while maintaining the piping at the temperature in itsoperating range, fixing the piping in the use position by fastening itat predetermined intervals to attachment members and by backfilling theearth about the pipe so that the pressure of the backfilled earth holdsthe piping in the position attained when it is brought to temperaturewithin the range of its operating temperature.

1. Method of mounting a hot water pipe in a district heating system in afixed position for use in conveying hot water which flows through thepiping at an operating temperature range of minimum to maximumtemperatures above the ambient temperature, comprising the steps oflocating a continuous length of piping from a source to a point of use,bringing the piping to a temperature within the range of its operatingtemperature by flowing hot water through the piping and permitting it tochange length freely in response to the temperature to which it isheated by the hot water, and while maintaining the piping at thetemperature in its operating rangE, fixing the piping in the useposition.
 2. Method, as set forth in claim 1, characterized by fixingthe piping in the use position by fastening it at predeterminedintervals to concrete attachment members.
 3. Method of mounting a hotwater pipe in a district heating system in a fixed position for use inconveying hot water which flows through the piping within an operatingtemperature range of minimum to maximum temperatures above the ambienttemperature, comprising the steps of locating a continuous length ofpiping in a position for use within an excavated earth trench from asource to a position of use, bringing the piping to a temperature withinthe range of its operating temperature by flowing hot water through thepiping and permitting it to change length freely in response to thetemperature to which it is heated by the hot water, and whilemaintaining the piping at the temperature in its operating range, fixingthe piping in the use position by fastening it at predeterminedintervals to attachment members and by backfilling the earth about thepipe so that the pressure of the backfilled earth holds the piping inthe position attained when it is brought to temperature within the rangeof its operating temperature.